When President Obama speaks at ground zero in Hiroshima on Friday, he must do more than recall the horrific consequences of the first atomic bombing… In a series of professional journal articles, Rutgers environmental scientist Alan Robock, University of Colorado atmospheric and oceanic scientist Owen Brian Toon and others document that the likely impact of a so-called “limited nuclear war” on climate and global food production would put the world’s population at grave risk of mass starvation.